Hydraulic control system and method

ABSTRACT

A hydraulic control system incorporating a variable displacement, pressure compensated hydraulic pump and means for varying the speed of the input shaft driving the variable displacement pump in proportion to the displacement of the pump.

BACKGROUND OF THE INVENTION

This invention relates to hydraulic control systems, and relates moreparticularly to pressure compensated type hydraulic control systems.

In certain applications of hydraulic power systems, pressure compensatedvariable displacement pumps have found utility by reducing the volume offlow discharged by the pump, and consequently the power required tooperate the pump, whenever the hydraulic flow requirements aresubstantially reduced. In aircraft, for instance, the major demand uponthe hydraulic system occurs during landing and takeoff when landinggear, flaps, etc. are operated. Throughout the remainder of the flightthe hydraulic flow demand requirements are substantially lower. Thepressure compensated pump automatically reduces its displacement inrelation to the flow demand requirements to reduce the power consumedduring this essentially "standby" condition. A drawback to such a systemhowever is that the pump is still operating at a relatively high,constant, speed and significant standby power consumption by the pumpstill occurs. Examples of prior art hydraulic systems are found in U.S.Pat. No. 1,576,153; 1,863,406; 2,425,958; 2,694,979; 2,752,858; and2,961,964.

It is a primary object of the present invention to provide an improvedhydraulic power system and method which utilizes not only a pressurecompensated pump to vary the flow developed by the pump in relation tothe demand requirements of the hydraulic system, but which alsosubstantially varies the rotational speed of the pump in relation to thedemand requirements to significantly reduce the power consumed by thehydraulic system when operating at less than maximum power demand.

More particularly, it is an important object of the present invention toprovide a pressure compensated pump which includes method and apparatusfor sensing pump displacement and varying the input shaft speed to thepump in relationship to pump displacement.

These and other objects and advantages of the present invention arespecifically set forth in or will become apparent from the followingdetailed description of preferred forms of the invention when read inconjunction with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic representation of a hydraulic control systemconstructed in accordance with the principles of the present invention;and

FIG. 2 is a schematic representation of another form of hydrauliccontrol system contemplated by the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now more particularly to FIG. 1, a hydraulic control systemgenerally denoted by the numeral 10 includes a source of pressurized gas12 delivering pressurized gas flow through a conduit 14 to a rotaryfluid turbine in the form of a centrifugal inflow gas turbine 16.Turbine 16 powers a rotary input shaft 18 appropriately mounted onbearings 20 to drive a variable displacement hydraulic pump generallydenoted by the numeral 22. The pump 22 illustrated is of the axialpiston type incorporating a cylinder barrel 24 operably driven by ashaft 18, and having a plurality of cylinders 26 therein. Mounted withineach cylinder 26 is a piston 28 whose outer end is engageable withininclinable swash plate 30. Upon rotation of barrel 24, the pistons 28move outwardly with respect to their associated cylinders 26 duringone-half of the revolution to draw in liquid flow from an input conduit32, and during the other half of the revolution the pistons 28 shiftinwardly into the associated cylinders 26 to displace pressurizedhydraulic liquid flow through an output port and conduit 34.

Pump 22 is of the pressure compensated type and includes a feedbackcontrol system comprising a conduit 36 communicating with output port34, and a pressure reducing valve 38 which is oppositely shiftablewithin a housing 40 to control communication of an output passage 42with either the pressurized output flow from the pump and conduit 36, ora low pressure reservoir drain 44. A biasing spring 46 urges valve 38rightwardly to communicate passage 42 with drain 44 and reduce thepressure maintained in passage 42, while pressure from the output 34 ofthe pump acts directly upon valve 38 to shift the latter leftwardly toconnect passage 42 with conduit 36 and increase the pressure in passage42.

Passage 42 communicates through a conduit 48 with a cylinder 50 definedwithin a housing 52, and an actuating piston 54 moves in response to thepressure developed in cylinder 50. A helical coil compression spring 56engages inclinable swash plate 30 to rotate the latter in a generallyclockwise direction about its bearing 31 to increase pump displacement,in opposition to the hydraulic force created upon piston 54 by pressurein chamber 50. Characteristically, spring 56 exerts a variable forceupon swash plate dependent upon the degree of compression of spring 56.Thus, the force exerted by spring 56 substantially increases as swashplate 30 rotates counterclockwise to a position reducing displacement ofpump 22. The feedback control provided by conduit 36, valve 38, andpiston 54 automatically develops a pressure within passage 42 andcylinder 50 that substantially balances the variable force exerted bycompression spring 56 and adjusts the displacement of pump 22 tomaintain a substantially constant output pressure in conduit 34. It isimportant to note that the feedback system develops a hydraulic pressurein passage 42 whose value is indicative of and varies substantiallyinversely in relation to the position of swash plate 30 and thedisplacement of pump 22. Such an arrangement of variable displacementpump 22 in combination with a pressure compensating feedback controlincluding pressure reducing valve 38 is well known, an example beingSperry-Vickers model PV3-240 pressure compensated pump.

Control system 10 further includes an element for controlling the speedof rotation of shaft 18 in the form of a butterfly gas flow controlvalve 58 interposed in conduit 14. Butterfly 58 is operably connectedthrough appropriate linkage 60 to a diaphragm 62 which traverses theinterior of a housing 64 to divide the interior into opposed gas fluidchambers 66 and 68. A biasing spring 70 urges diaphragm 62 upwardlytoward an adjustable limit stop 71 whose position is externallyadjustable via the nut associated therewith. Pressure of gas flowdownstream of butterfly valve 58 is transmitted through conduit 72 intochamber 68 to exert a pneumatic force on the diaphragm assisting spring70 and urging valve 58 to move toward a more closed position reducingrate of gas flow to turbine 16 and thereby reducing the speed ofrotation of shaft 18.

An opposing force on diaphragm 62 is created by higher pressurized gasflow transmitted to chamber 66 from conduit 14 at a location upstream ofvalve 58, across a pilot pressure regulator 76, a three-way pneumaticcontrol valve 78, and a conduit 74. Valve 78 includes a verticallyshiftable plunger 80 which effectively controls fluid communication ofconduit 74 with both the higher pressure conduit 14 and low pressureexhaust passage 79. Plunger 80 is vertically adjustable within a housing82 having a diaphragm 84 traversing a portion of the interior thereof todefine a closed gas receiving chamber 86 communicating with conduit 72.A spring 88 exerts a force on diaphragm 84 opposing the pneumatic forcecreated by gas in chamber 86.

At the upper end of housing 82 there is formed an interior liquidreceiving chamber 90 communicating with passage 42 through anappropriate conduit 92. A piston 94 carried at the upper end of plunger80 is vertically movable within chamber 90 in response to the liquidpressure developed in passage 42 and chamber 90.

In operation of the FIG. 1 system, pressurized gas flow from source 12which, for instance, may be the bleed air flow from a turbofan engine inan aircraft, is metered by butterfuly valve 58 and delivered to conduit14 to effect rotation of turbine 16 and shaft 18. In response, thevariable displacement hydraulic pump 22 draws in liquid at low pressurefrom its intake conduit 32, and delivers pressurized hydraulic fluidflow through its output port 34. Once output pressure from the pumpreaches a preselected level, the hydraulic force exerted upon pressurereducing valve 38 is sufficient to urge valve 38 leftwardly and deliverpressurized liquid through conduits 48 and 92 to liquid chambers 50 and90 respectively. In response, swash plate 30 is rotated until a positionis reached wherein the output flow capacity of the pump substantiallymatches the hydraulic control system demand requirements as evidenced byestablishing a substantially constant output pressure from the pump. Inaccomplishing this, the pressure regulating valve 38 establishes apressure in passage 42 and chamber 50 which substantially balances thevariable force exerted by the linear gradient spring 56. In so doing, acharacteristic pressure is developed in passage 42 dependent upon theangular position of swash plate 30 and thus the displacement of pump 22.A typical application of the system for instance, develops a pressure inpassage 42 which varies from approximately 600 psi to approximately 1000psi as swash plate 30 shifts from its maximum displacement positionillustrated to a minimum displacement position wherein swash plate 30 isapproximately perpendicular to piston 28. Thus, the pressure developedin passage 42 is indicative of the angular position of swash plate 30and the displacement of pump 22, varying substantially inverselythereto.

This characteristic pressure also exerts a hydraulic force on piston 94to variably position plunger 80 in relation to the pump displacement.For instance, as pump displacement decreases and pressure in passage 42and chamber 90 accordingly increases, plunger 80 is shifted downwardlyin FIG. 1 to increase flow from conduit 74 to conduit 79 and reduce thepneumatic pressure maintained in chamber 66. As a result, the force ofspring 70 and pressure of gas in chamber 68 rotates butterfly valve 58to a more closed position to reduce gas flow to turbine 16. Accordingly,the speed of rotation of shaft 18 reduces as pump displacement reduces.In this manner, it will be seen that the present invention provides animproved control system wherein the speed of rotation of shaft 18 isvaried in relation to, and preferably substantially directlyproportional to the displacement of pump 22. Accordingly, in essentiallystandby condition wherein the hydraulic flow demand is at a minimum andthe pump swash plate 30 is stroked to a substantially perpendicularposition to minimize pump displacement, speed of rotation of shaft 18also substantially reduces in order to minimize the power consumed inoperating pump 22 in the standby condition. In this manner, theinvention affords greater safety particularly in aircraft applications,since it becomes practical and efficient to permit a plurality of pumpssuch as pump 22 to operate while in a standby condition with minimumpower consumption. A substantial increase in operating efficiencythroughout the cycle of operation of the aircraft is also realized.

In conjunction with the controls of the present invention, conventionalflow controls can be incorporated. For instance, the system illustratedincludes pneumatic pressure balance controls effected by the delivery ofpneumatic gas flow to chambers 66 and 68 from opposite sides ofbutterfly valve 58. Accordingly, the diaphragm 62 is operable tonormally maintain the gas flow through conduit 14 at a substantiallyconstant level, yet capable of being overridden by a significant changein liquid pressure developed within chamber 90. A further controlincluded in the system illustrated is a maximum pressure control in theform of the pressurized gas flow delivered to chamber 86 to oppose theforce created by compression spring 88. If, for instance, the absolutepressure of gas being delivered to turbine 16 becomes excessively high,diaphragm 84 is shifted downwardly against the urgings of spring 88 torestrict the flow of pressurized gas into conduit 74 and thus cause thebutterfly 58 to shift to a more closed position and prevent overpressurization in conduit 14 and/or over speed of shaft 18.

FIG. 2 illustrates a modified form of the system contemplated by thepresent invention which incorporates a substantial number of the sameelements as depicted and described in detail above with respect to FIG.1 as denoted by utilization of like numerals for like elements. Incontrast to the FIG. 1 arrangement, however, the FIG. 2 arrangementcontemplates a drive for shaft 18 which includes a shaft 101mechanically driven by a prime mover engine 100. Shafts 101 and 18 arerespectively input and output shafts of a conventional hydraulic torqueconverter 102. This system further includes a hydraulic fluid supplypump 104 which delivers fluid to fill the torque converter 102. Fluidfrom the torque converter is drained through an exhaust conduit 106 andacross metering valve 108 to a low pressure reservoir 110.

As well known within the art, torque converter 102 transmits a varyingquantity of torque to shaft 18 to operate it at different speeds, alldependent upon the volume of hydraulic fluid contained within the torqueconverter. The present invention contemplates the variable control offluid exhaust from torque converter 102 to effect change of speed ofshaft 18. To this end, the conduit 92 communicating with the passage 42of the hydraulic feedback control of the pressure compensator pump 22 isdelivered to operate directly against valve 108 in opposition to abiasing spring 114. Valve 108 is laterally shiftable back and forth suchthat its metering notch 112 can variably control the rate of exhaustflow from torque converter 102 to reservoir 110.

In operation of the FIG. 2 arrangement, at high pump displacements whereswash plate 30 is stroked to a high inclination as illustrated, pressurein passage 42 is at a minimum thereby allowing valve 108 to be shiftedto a rightward location placing a substantial restriction to exhaustflow from torque converter 102. Accordingly, the torque converter 102remains substantially filled and maximum torque is delivered to driveshaft 18 at a maximum speed. As pump displacement decreases when swashplate 30 is stroked to a more vertical inclination, pressure in passage42 builds to a higher level as described previously with respect to FIG.1, and valve 108 accordingly shifts leftwardly to allow greater exhaustflow from torque converter 102. The volume of hydraulic fluid thusmaintained within converter 102 substantially reduces to reduce theamount of torque delivered to shaft 18 and substantially lower the speedof shaft 18. Accordingly it will be seen that the FIG. 2 arrangementoperates similarly to the FIG. 1 arrangement in varying the speed ofinput shaft 18 in relation to the displacement of a pressure compensatedpump 22.

From the foregoing it will be apparent that the present invention alsocontemplates an improved method of controlling a variable displacementhydraulic pump 22 driven by variable speed shaft 18, which includes thesteps of sensing pump output pressure in output port 34 as well assensing the pump displacement as evidenced by the pressure developed inpassage 42. Pump displacement is controlled in relation to the outputpressure in order to maintain a substantially constant output pumppressure, and the speed of shaft 18 is controlled in relation to thesensed pump displacement.

The foregoing detailed description of preferred forms of the inventionshould be considered exemplary in nature and not as limiting to thescope and spirit of the invention as set forth in the appended claims.

Having described the invention with sufficient clarity that thoseskilled in the art may make and use it, I claim:
 1. Apparatus forcontrolling a variable displacement hydraulic pump driven by a variablespeed input shaft to develop a pressurized output fluid flow andincluding an element adjustably positionable to vary pump displacement,comprising:first sensing means for sensing pressure of said pump outputflow; first control means for adjusting the position of said element inresponse to said first sensing means; second sensing means for sensingsaid position of the element; and second control means responsive tosaid second sensing means for adjusting the speed of said shaft inproportion to said sensed position.
 2. In combination:a source ofpressurized fluid; a rotary turbine driven by pressurized fluid fromsaid source and having a rotary power output shaft; a control valve forvarying the flow of fluid from said source to said turbine to controlthe speed of rotation of said shaft; a variable displacement liquid pumpoperably driven by said shaft and having a liquid output port; anelement for adjusting the displacement of said pump; compressiblebiasing means urging said element in a direction increasing pumpdisplacement and exerting a force on said element which decreases inrelation to increase in said pump displacement; a control cylinderhaving a liquid chamber and a piston reciprocal within said chamberurging said element in a direction decreasing pump displacement; afeedback control communicating with said output port and operable tometer liquid flow to said liquid chamber to shift said piston and varysaid displacement of the pump to maintain a substantially constantpressure of liquid delivered from said output port, said feedback meansdeveloping a variable pressure in said liquid chamber which isindicative of pump displacement; and actuator means responsive to saidvariable pressure in said liquid chamber for adjusting said controlvalve to change the speed of rotation of said shaft substantially inproportion to pump displacement.
 3. A hydraulic power systemcomprising:a source of pressurized gas; a power input shaft; a rotarypower turbine driven by said source of pressurized gas and operablycoupled to drive said shaft; a control valve for controlling flow of gasfrom said source to said turbine to vary the speed of said shaft; apneumatic actuator having a gas chamber operably coupled to actuate saidcontrol valve in relation to the pneumatic pressure in said gas chamber;a variable displacement hydraulic pump driven by said shaft and having afluid output port; pressure sensing means for sensing the hydraulicpressure of fluid delivered from said output port of the pump; meansresponsive to said pressure sensing means for adjusting the displacementof said pump to maintain said hydraulic pressure at a substantiallyconstant preselected level; displacement sensing means for sensing saiddisplacement of the pump; and a three-way valve operably communicatingwith said source and a low pressure gas return, said three-way valveoperably coupled with said displacement sensing means and said gaschamber to control communication of said gas chamber with said sourceand said low pressure return to vary the magnitude of said pneumaticpressure in the gas chamber in relation to said displacement of the pumpwhereby said speed of the shaft is varied in relation to saiddisplacement.
 4. A method of controlling a variable displacementhydraulic pump driven by a variable speed input shaft and having anelement adjustably positionable to vary pump displacement, comprisingthe steps of:sensing pump output pressure; positioning said element inrelation to said sensed output pressure; sensing the position of saidelement; and controlling input shaft speed in proportion to said sensedposition.
 5. A method as set forth in claim 4, wherein said position ofthe element is controlled to maintain a substantially constant,preselected pump output pressure.
 6. A method as set forth in claim 5,wherein input shaft speed is controlled by varying motive gas flow to agas turbine driving said shaft.
 7. A method as set forth in claim 6,wherein said input shaft speed is incrementally varied through a rangeof speeds.
 8. A hydraulic power system comprising:a power input shaft; avariable displacement hydraulic pump driven by said shaft and having afluid output port; a first element variably positionable to adjust thedisplacement of said pump; a second element for adjusting the speed ofsaid input shaft; first control means for sensing pressure of fluiddelivered from said output port of the pump and accordingly adjustingthe position of said first element to maintain said pressure at asubstantially constant preselected level; and second control means forsensing said position of the first element and accordingly operatingsaid second element to adjust said speed of the input shaft in relationto said sensed position.
 9. A system as set forth in claim 8, furtherincluding a source of pressurized fluid, a rotary power turbine operablycoupled to said shaft whereby pressurized fluid delivered from saidsource to said turbine rotates said shaft, said second elementcomprising a valve for variably controlling flow from said source tosaid turbine in relation to said sensed position.
 10. A system as setforth in claim 8, further including a hydraulic torque converteroperably coupled to deliver a variable amount of power to said shaft inrelation to the volume of hydraulic fluid within said torque converter,said second element comprising means for adjusting said volume ofhydraulic fluid in said torque converter in relation to said sensedposition.
 11. A system as set forth in claim 8, wherein said variabledisplacement hydraulic pump comprises an axial piston pump having arotary barrel, a plurality of pistons reciprocal within said barrel,said first element comprising an inclinable swash plate engaging saidpistons to vary the length of stroke of said pistons in relation to theinclination of said swash plate.
 12. A system as set forth in claim 11,wherein said first control means comprises a cylinder defining a fluidcontrol chamber, a piston mounted within said fluid control chamber andengageable with said swash plate to vary the inclination thereof, and apressure reducing valve operably communicating said fluid controlchamber with said output port and a low pressure fluid return, saidpressure reducing valve responsive to pressure in said output port toselectively vary the pressure developed within said fluid controlchamber whereby said variable pressure in the fluid control chamber isindicative of the inclination of said swash plate.
 13. A system as setforth in claim 12, wherein said second control means includes a pressureresponsive plunger shiftable to vary the speed of said input shaft,there being a housing defining a cylinder in which said plungerreciprocates, conduit means interconnecting said fluid control chamberand said plunger cylinder, and a spring urging said plunger inopposition to pressure in said plunger cylinder whereby said plungershifts in relation to the magnitude of said variable pressure developedwithin said fluid control chamber.
 14. A system as set forth in claim13, further including a source of pressurized gas, a rotary power gasturbine operably coupled to drive said shaft, a first gas conduit fordelivering pressurized gas flow from said source to said turbine torotate said shaft, said second element comprising a control valveoperably interposed in said first gas conduit to adjust gas flowdelivered from said source to said turbine.
 15. A hydraulic power systemcomprising:a source of pressurized gas; a power input shaft; a rotarypower gas turbine operably coupled to drive said shaft; a first gasconduit for delivering pressurized gas flow from said source to saidturbine to rotate said shaft; a variable displacement hydraulic pumpdriven by said shaft and having a fluid output port, said pumpcomprising an axial piston pump having a rotary barrel and a pluralityof pistons reciprocal within said barrel; a first element for adjustingthe displacement of said pump comprising an inclinable swash plateengaging said pistons to vary the length of stroke of said pistons inrelation to the inclination of said swash plate; a second element foradjusting the speed of said input shaft comprising a control valveoperably interposed in said first gas conduit to adjust gas flowdelivered from said source to said turbine; first control means forsensing pressure of fluid delivered from said output port of the pumpand accordingly operating said first element to maintain said pressureat a substantially constant preselected level, said first control meanscomprising a cylinder defining a fluid control chamber, a piston mountedwithin said fluid control chamber and engageable with said swash plateto vary the inclination thereof, and a pressure reducing valve operablycommunicating said fluid control chamber with said output port and a lowpressure fluid return, said pressure reducing valve responsive topressure in said output port to selectively vary the pressure developedwithin said fluid control chamber whereby said variable pressure in thefluid control chamber is indicative of the inclination of said swashplate; second control means for sensing said displacement of the pumpand accordingly operating said element to adjust said speed of the inputshaft in relation to said displacement, said second control meansincluding a cylinder, pressure responsive plunger reciprocal in saidcylinder to vary the speed of said input shaft, conduit meansinterconnecting said fluid control chamber and said cylinder, and aspring urging said plunger in opposition to pressure in said cylinderwhereby said plunger shifts in relation to the magnitude of saidvariable pressure developed within said fluid control chamber; and ahousing associated with said control valve, a diaphragm operably coupledto said control valve and traversing said housing to divide the latterinto opposing gas chambers, said second control means further includinga shiftable three-way carried by said plunger for variably communicatingone of said opposing gas chambers with pressurized gas flow in saidfirst gas conduit and a low pressure return whereby to develop apneumatic pressure in said one of the opposing gas chambers whosemagnitude is indicative of the magnitude of pressure in said fluidcontrol chamber.
 16. A system as set forth in claim 15, furtherincluding a second gas conduit interconnecting the other of saidopposing gas chambers with said first gas conduit at a locationdownstream of said control valve, and spring means in said other of theopposing gas chambers assisting pressure of gas therein in urging saiddiaphragm to shift in a direction causing said control valve to move ina direction decreasing gas flow to said turbine.
 17. A system as setforth in claim 16, further including a stop for limiting travel of saiddiaphragm in a direction decreasing gas flow through said first gasconduit.
 18. A system as set forth in claim 17, further including meansfor adjusting the position of said stop.
 19. In combination:a source ofpressurized fluid; a rotary turbine driven by pressurized fluid fromsaid source and having a rotary power output shaft; a control valve forvarying the flow of fluid from said source to said turbine to controlthe speed of rotation of said shaft; a variable displacement liquid pumpoperably driven by said shaft and having a liquid output port; anelement for adjusting the displacement of said pump; compressiblebiasing means urging said element in a direction increasing pumpdisplacement and exerting a force on said element which decreases inrelation to increase in said pump displacement; a control cylinderhaving a liquid chamber and a piston reciprocal within said chamberurging said element in a direction decreasing pump displacement; afeedback control communicating with said output port and operable tometer liquid flow to said liquid chamber to shift said piston and varysaid displacement of the pump to maintain a substantially constantpressure of liquid delivered from said output port, said feedback meansdeveloping a variable pressure in said liquid chamber which isindicative of pump displacement; and actuator means responsive to saidvariable pressure in said liquid chamber for adjusting said controlvalve to change the speed of rotation of said shaft substantially inproportion to pump displacement, said actuator means including ahousing, a diaphragm operably coupled to shift said control valve andtraversing said housing to divide the latter into opposed fluidreceiving chambers, a three-way metering valve for variably meteringpressurized fluid flow from said source into and out of one of saidopposed fluid chambers to shift said control valve, a spring urging saidthree-way metering valve in a direction increasing pressure in said oneof the opposed chambers to thereby increase the flow of pressurizedfluid to said turbine and increase said shaft speed, and meanscommunicating the variable pressure maintained in said liquid chamber tosaid metering valve whereby said variable pressure exerts a force onsaid metering valve urging the latter in a direction reducing pressuremaintained in said one of the opposed chambers to thereby decrease fluidflow to said turbine and decrease shaft speed.
 20. A combination as setforth in claim 19, further including spring means in the other of saidopposed chambers urging said diaphragm in a direction decreasing fluidflow to said turbine, and a conduit communicating said other of theopposed chambers with fluid flow being delivered to said turbine at alocation downstream of said control valve.
 21. A combination as setforth in claim 20, wherein said feedback control includes a pressurereducing valve shiftable in first and second directions to respectivelycommunicate said liquid chamber with said output port and a low pressuredrain, there being a spring urging said pressure reducing valve in saidfirst direction, the pressure developed in said output port urging saidpressure reducing valve in said second direction.